Pre-blend cement compositions containing non-chloride accelerators

ABSTRACT

The present invention relates to pre-blend cement for general-purpose concrete construction containing Class-F fly ash, Class-C fly ash or slag, and less than about 5 percent (w/w) of sodium thiocyanate (NaSCN) and/or calcium nitrate (Ca(NO 3 ) 2 ), as a substantial replacement for cement. The sodium thiocyanate and/or calcium nitrate are additives for improved high early strength and accelerated setting times, thereby allowing the concrete structure to be put into service sooner, reducing labor cost, and allowing precast concrete and concrete masonry manufacturers to achieve rapid form and mold turnover.

FIELD OF THE INVENTION

The present invention relates to pre-blend compositions for generalpurpose concrete mixes, and more particularly to pre-blend compositionscontaining additives for shortened setting times that meet ASTM C595specification for pre-blend cements.

BACKGROUND OF THE INVENTION

The present invention is concerned with the utilization of non-chlorideadditives, namely sodium thiocyanate (NASCN) and/or calcium nitrate(Ca(NO₃)₂), for shortening the setting times of concrete ready-mixes.Further, the invention is also concerned with the utilization of threeindustrial by-products; namely, Class-F fly ash, Class-C fly ash, andblast furnace slag in general purpose concrete-making compositions.

When finely divided or pulverized coal is combusted at hightemperatures, for example, in boilers for the steam generation ofelectricity, the ash, consisting of the incombustible residue plus asmall amount of residual combustible matter, is made up of twofractions, a bottom ash recovered from the furnace or boiler in the formof a slag-like material and a fly ash which remains suspended in theflue gases from the combustion until separated therefrom by knownseparation techniques, such as electrostatic precipitation. This fly ashis an extremely finely divided material generally in the form ofspherical bead-like particles, with at least 70% by weight passing a 200mesh sieve, and has a generally glassy state resulting from fusion orsintering during combustion. As recognized in the American Society ofTesting Materials (ASTM) specification designations C618-00 entitled“Fly Ash and Raw or Calcined Natural Pozzolan for Use as a MineralAdmixture in Portland Cement Concrete” and D5370-96 entitled “StandardSpecification for Pozzolanic Blended Materials in ConstructionApplication,” fly ash is subdivided into two distinct classifications;namely, Class-F and Class-C. The definitions of these two classes givenin the aforementioned ASTM specifications are as follows:

“Class-F—Fly ash normally produced from burning anthracite or bituminouscoal that meets the applicable requirements for this class as givenherein. This class fly ash has pozzolanic properties.

Class-C—Fly ash normally produced from lignite or subbituminous coalthat meets the applicable requirements for this class as given herein.This class of fly ash, in addition to having pozzolanic properties, alsohas some cementitious properties. Some Class-C fly ashes may containlime contents higher than 10%.”

The latter reference to “pozzolanic properties” refers to the capabilityof certain mixtures that are not in themselves cementitious, but arecapable of undergoing a cementitious reaction when mixed with calciumhydroxide in the presence of water. Class-C fly ash possesses directcementitious properties as well as pozzolanic properties. ASTM C618-00is also applicable to natural pozzolanic materials that are separatelyclassified as Class N but are not pertinent here.

As the above quotation from the ASTM specification indicates, the typeof coal combusted generally determines which class fly ash results, andthe type of coal in turn is often dependent upon its geographic origin.Thus, Class-C fly ash frequently results from the combustion of coalsmined in the Midwest United States; whereas Class-F fly ash often comesfrom combustion of coals mined in the Appalachian region of the UnitedStates. The ASTM specification imposes certain chemical and physicalrequirements upon the respective fly ash classifications which are setforth in U.S. Pat. No. 5,520,730, the disclosure of which isincorporated herein by reference.

Blast furnace slag is a by-product of the production of iron in a blastfurnace; silicon, calcium, aluminum, magnesium and oxygen are the majorelemental components of slag. Blast furnace slags include air-cooledslag resulting from solidification of molten blast furnace slag underatmospheric conditions; granulated blast furnace slag, a glassy granularmaterial formed when molten blast furnace slag is rapidly chilled as byimmersion in water; and pelletized blast furnace slag produced bypassing molten slag over a vibrating feed plate where it is expanded andcooled by water sprays, whence it passes onto a rotating drum from whichit is dispatched into the air where it rapidly solidifies to sphericalpellets. In general the glass content of the slag determines thecementitious character. Rapidly cooled slags have a higher glass contentand are cementitious; slowly cooled slags are non-glassy and crystallineand, thus do not have significant cementitious properties.

The quantities of these by-product materials that are produced annuallyare enormous and are likely only to increase in the future. As petroleumoil as the fuel for the generation of electricity is reduced because ofconservation efforts and unfavorable economics, and as politicalconsiderations increasingly preclude the construction of new nuclearpower electrical generating facilities, or even the operation orcontinued operation of already completed units of this type, greaterreliance will necessarily fall on coal as the fuel for generatingelectricity. As of 1979, the volume of Class-F fly ash that wasavailable then was estimated to be about five times what could bereadily utilized. The estimated annual total production of coal ash inthe U.S. is about 66.8 million tons, while the annual total coal ashsales in the U.S. is only about 14.5 million tons. Further, in Canada,the recovery of copper, nickel, lead and zinc from their ores producesover twelve million tons of slag per year, which is usually accumulatednear the smelters with no significant use. Obviously, there is an urgentand growing need to find effective ways of employing these unavoidableindustrial by-products since they will otherwise collect at a staggeringrate and create crucial concerns regarding their adverse environmentaleffects.

Various proposals have already been made for utilizing both types of flyash. According to Lea (1971), The Chemistry of Cement and Concrete,Chemical Publishing Company, Inc., page 421 et seq., fly ash, i.e.,Class-F type, from boilers was first reported to be potentially usefulas a partial replacement for Portland cement in concrete constructionabout 50 years ago, and its utilization for that purpose has sincebecome increasingly widespread. It is generally accepted that theproportion of Portland cement replaced by the usual fly ash should notexceed about 20% to avoid significant reduction in the compressivestrength of the resultant concrete, although some more cautiousjurisdictions may impose lower limits, e.g., the 15% maximum authorizedby the Virginia Department of Highways and Transportation (VDHT). Asdescribed in Lea on page 437, the substitution of fly ash tends toretard the early rate of hardening of the concrete so that the concreteexhibits up to a 30% lower strength after seven days testing and up to a25% lower strength after 28 days of testing, but in time the strengthlevels normalize at replacement levels up to 20%. Increasing thesubstitution quantity up to 30% gives more drastic reduction in theearly compression values as well as an ultimate strength reduction of atleast about 15% after one year.

The limited substitution of fly ash for Portland cement in concreteformulations has other effects beyond compressive strength changes, bothpositive and negative. The fly ash tends to increase the workability ofthe cement mix and is recognized as desirably reducing the reactivity ofthe Portland cement with so-called reactive aggregates. On the otherhand, fly ash contains a minor content of uncombusted carbon that actsto absorb air entrained in the concrete. Because entrained air desirablyincreases the resistance of the hardened concrete to freezing, suchreduction in entrained air is undesirable, but can be compensated for bythe inclusion as an additive of so-called air-entraining agents.

Dodson, et al. in U.S. Pat. No. 4,210,457, while recognizing theaccepted limit of 20% replacement with fly ash of the Portland cement inconcrete mixes, proposes the substitution of larger amounts, preferably50% or more, of the Portland cement with particular selected fly asheshaving a combined content of silica, alumina and ferric oxide content,less than 80% by weight, and a calcium oxide content exceeding 10%,based on five samples of such ashes, varying from about 58-72% combinedwith a calcium oxide range of about 18-30%. Six other fly ash samplesthat are not suitable at the high replacement levels of 50% or more wereshown to vary in the combined oxide content from about 87-92% and incalcium oxide content from about 4% to about 8%. Evaluating these valuesagainst the ASTM C618-00, one observes that the acceptable fly ashescome under the Class-C specifications, while the unacceptable ashes fellwithin the Class-F specification. Thus, Dodson, et al. in effectestablish that Class-C fly ashes are suitable for substantially higherlevels of replacement for Portland cement in concrete mixes than areClass-F fly ashes, and this capacity is now generally recognized, withClass-C fly ashes being generally permitted up to about a 50%replacement level while maintaining the desirable physical properties ofthe concrete, especially compressive strength.

In U.S. Pat. No. 4,240,952, Hulbert, et al. while also acknowledging thegenerally recognized permissible limit of Class-F fly ash replacementfor Portland cement of 20%, propose replacement of at least 50% and upto 80%, provided the mix contains as special additives about 2% ofgypsum and about 3% of calcium chloride by weight of the fly ash. Thefly ash described for this purpose, however, was a Class-C fly ashanalyzing about 28% calcium oxide and combined silica, alumina andferric oxide content of about 63%. With up to 80% of this fly ash andthe specified additives, compressive strengths comparable to straightPortland cement were said to be generally achievable. In one exampleusing 140 pounds Portland cement and 560 pounds of fly ash (20:80 ratio)with conventional amounts of coarse and fine aggregate, and water andincluding the requisite additives, compressive strengths tested at 3180psi for 7 days, 4200 psi for 14 days and about 5000 psi at 28 days.

In U.S. Pat. Nos. 4,018,617 and 4,101,332, Nicholson proposed the use ofmixtures of fly ash (apparently Class-F in type), cement kiln dust andaggregate for creating a stabilized base supporting surface replacingconventional gravel or asphalt aggregate stabilized bases in roadconstruction wherein the useful ranges were fly ash 6-24%, CKD (cementkiln dust) 4-16% and aggregate 60-90%, with 8% CKD, 12% fly ash and 80%aggregate preferred. Compressive strength values for such measures asrevealed in the examples varied rather erratically and generallyexhibited only small increases in compressive strength over the 7 to 28day test period. Among the better results were for the preferred mixturewherein the values increased from about 1100 psi at 7 days to 1400 psiat 28 days. The addition of a small amount of calcium chloride improvedthose values by about 200 psi. On the other hand, the addition of 3% oflime stack dust recovered from a lime kiln significantly reduced theresults to about 700 psi at 7 days to 900-1300 psi at 28 days.Elimination of the aggregate reduced the strength to a fraction of thevalues otherwise obtained, a mixture of 12% CKD and 88% fly ash aloneshowing strength values of only about 190-260 psi over the 28-day testperiod. Similarly, the choice of a finely divided aggregate such as fillsand resulted in about the same fractional level of strength values inthe range of about 140-230 psi. A combination of finely divided andcoarse aggregate in approximately equal amounts reduced the compressivestrength values by about 50% with virtually no change over the testperiod, giving values ranging from 650-750 psi, except where 1% of Type1 Portland cement was included which restored the strength values toabout their original level, except at the initial 7 days period wherethe strength values were about 800-900 psi, increasing at 28 days toabout 1200-1600 psi. Curiously, the best strength results were attainedwhen 11.6% fly ash was combined with 3.4% lime with the balance crushedaggregate, the CKD being omitted entirely, for which the strength valueswhile starting at a lower level of about 850-950 at 7 days increased toabout 1700 psi at 28 days.

The combination of fly ash and lime stack dust incidentally mentioned inthe later patent was explored further by Nicholson in U.S. Pat. No.4,038,095 which concerns mixtures of about 10-14% fly ash, about 5-15%lime stack dust with the balance aggregate in the range of 71-85%.Somewhat inexplicably, the compressive results reported here for suchmixtures do not reach the high level specified in the first twoaforementioned Nicholson patents, the strength values specified beingonly about 1000 psi with the more general levels well below thatdepending on particular proportions.

In U.S. Pat. No. 4,268,316, Wills, Jr. discloses the use of mixtures ofkiln dust and fly ash as a replacement for ground limestone and gypsumfor forming a mortar or masonry cement, using proportions of about25-55% Portland cement, about 25-65% CKD and 10-25% fly ash. When thesemortar formulations were mixed with damp sand in the proportions ofabout one part cement mixture to 2.5-3 parts sand, compression strengthscomparable to those of standard masonry cement composed of 55% cementclinkers, 40% limestone and 5% gypsum were shown for mixtures containing50% cement, 24-40% CKD and 15-25% fly ash. Inexplicably, in one example,when the cement content was increased to 55% with 35% CKD and 10-% flyash, the compressive strengths dropped by about 30-40% at both the 7 dayand 28 day ages to levels inferior to the standard material. As thecement content was decreased, with corresponding increases in the CKD,the compressive strength values dropped drastically. On the other hand,in another similar example, mixtures containing 55% cement, 35% CKD and10% fly ash proved superior in compressive strength, particularly at the28 day age, to mixtures containing 50% cement, 35% fly ash and 15% CKD,as well as other standard masonry cements containing 50% cement, 47%limestone and 3% gypsum. Indeed, strength values dropped about 40% forthe mixtures having a 5% reduction in cement and a corresponding 5%increase in the fly ash to values definitely inferior to the standardcements. Similar variations were shown under laboratory test conditionsfor comparable 50/35/15 mixtures dependent on the source of the fly ashwhile under actual construction conditions for the same mixtures,compressive strength values were reduced by about 50% for both theconventional masonry cement containing 55% Portland cement andcomparable mixtures within the patented concept. The fly ash here waspreferably Class-F with Class-C materials being less desirable.

In U.S. Pat. No. 4,407,677, Wills, Jr. went on to teach that in themanufacture of concrete products such as blocks or bricks, the fly ashusually employed in combination with Portland cement therein could bereplaced in its entirety by CKD with modest improvement in earlycompressive strength values for such products. Thus, at one-day andtwo-day tests compressive strength values of about 500-800 psi wereshown, but were said to increase to about 1200 psi after 28 days. Themixes disclosed in Wills, Jr. '677 contained 0.4-0.9 parts cement, about0.1-0.6 parts CKD and 10-12 parts aggregate combining both fine andcoarse materials, such as expanded shale and natural sand in a weightratio of 80/20. Masonry cements generally develop at least about 95% oftheir strength properties at 28 days age so that additional aging of thepatented products would not be expected to result in any significantincrease in their compressive strength values.

U.S. Pat. Nos. 5,520,730 and 5,266,111 of the present inventor, disclosea general-purpose concrete composition comprising Portland cement,Class-F fly ash, and CKD. The patents also disclose a “synthetic Class-Cfly ash blend” comprising Class-F fly ash and CKD. These patentsdisclose the advantages of early strength of concrete; however,utilization of sodium thiocyanate and/or calcium nitrate as a cementadditives are not disclosed.

U.S. Pat. No. 6,008,275 to Moreau et al. discloses a cement compositioncomprising greater than about 10% by weight of a pozzolanic cementreplacement based on the weight of said hydraulic cement and cementreplacement, and a polycarboxylate polymer. The composition can alsocontain an accelerator such as calcium nitrate and sodium thiocyanate.The pozzolanic replacement material can be fly ash, class C and/or classF; blast furnace slag; calcine clay; and natural pozzolan materials. Theamounts of calcium nitrate and sodium thiocyanate used by Moreau et al.are impractical and do not meet ASTM specifications for pre-blendcement. Further, the compositions of Moreau et al. are not pre-blendcements and are wet concrete mixtures.

U.S. Pat. No. 4,606,770 to Gerber discloses a cement mix includinghydraulic cement, aggregate, sufficient water to affect hydraulicsetting of the cement, and an additive comprising an N-methylol amide,specifically, tri- or tetramethylolglycoluril alone or in combinationwith other accelerators, such as calcium nitrate and sodium thiocyanate.The additive is present in an amount sufficient to decrease the timenecessary for the hardening of the concrete mix. The compositions ofGerber are not pre-blend cements and are wet concrete mixtures.

U.S. Pat. No. 5,531,825 to Gartner et al. discloses a cementset-accelerating admixture and compositions containing such admixtures.The admixture compositions comprise one or more nitroalcohols present inan amount effective to increase the set acceleration of a hydrauliccement composition. The invention further comprises one or moreconventional accelerators, including calcium nitrate and sodiumthiocyanate. Gartner et al. disclose only pastes, mortars and concretecompositions, but fail to mention a pre-blend composition.

None of the above patents disclose pre-blend cement compositions forfast settling times, meeting ASTM Designations C 595 specifications forpre-blend cements; therefore, there remains a need for pre-blend cementmixes with fast setting times, because the addition of fly ash or slagto concrete often results in slow setting. There are many advantages forfast setting times, such as allowing the concrete structure to be putinto service sooner, thereby reducing labor cost, and allowing pre-castconcrete and concrete masonry manufacturers to achieve rapid form andmold turnover.

SUMMARY OF THE INVENTION

Applicant has discovered an optimal range of non-chloride accelerators,namely sodium thiocyanate and/or calcium nitrate, for use with pre-blendcement (also referred to as blended cement) compositions. The optimalrange of sodium thiocyanate and/or calcium nitrate is less than about 5percent by weight, preferably from about 0.2 percent to about 4 percentby weight, in a pre-blend composition. Above about 5 percent of sodiumthiocyanate, the accelerator advantage is no longer effective; and aboveabout 5 percent of calcium nitrate, the cement composition does not meetASTM C595 specification. Further, because sodium thiocyanate and calciumnitrate are hygroscopic, using greater than about 5 percent in apre-blend cement yields an undesirable mix because of water absorptionproblems. Therefore, it is critical that the concentration of sodiumthiocyanate and/or calcium nitrate in the pre-blend composition ismaintained at less than about 5 percent by weight. Within this range,however, the amount of non-chloride accelerators can be varied toachieve desired set times. For example, the pre-blend cement can beadjusted to accommodate seasonal uses. In the summer, the pre-blendshould contain a lower amount of non-chloride accelerator(s) because thecement naturally sets faster in the summer heat. Alternatively, in thewinter, the pre-blend should contain a higher amount of non-chlorideaccelerator(s) because the cold naturally retards the cement settingrate.

An objective of the present invention is to provide a pre-blend cementcomposition for improved early strength containing cement and sodiumthiocyanate and/or calcium nitrate. In a preferred embodiment, cement ispresent in an amount greater than about 50% by weight; sodiumthiocyanate and/or calcium nitrate are present in an amount of less thanabout 5 percent by weight (w/w).

A further objective of the present invention is to provide a pre-blendcement composition for improved early strength containing cement,Class-F fly ash, and sodium thiocyanate and/or calcium nitrate. In apreferred embodiment; cement is present in an amount greater than about50% by weight; Class-F fly ash is present in an amount of about 20percent to about 30 percent by weight; and sodium thiocyanate and/orcalcium nitrate is present in an amount of less than about 5 percent byweight.

A further objective of the present invention is to provide a pre-blendcement composition for improved early strength containing cement,Class-C fly ash, and sodium thiocyanate and/or calcium nitrate. In apreferred embodiment; cement is present in an amount greater than about50% by weight; Class-C fly ash is present in an amount of about 20percent to about 30 percent by weight; and sodium thiocyanate and/orcalcium nitrate is present in an amount of less than about 5 percent byweight.

A further objective of the present invention is to provide a pre-blendcement composition for improved early strength comprising cement,Class-C fly ash, Class-F fly ash, and sodium thiocyanate and/or calciumnitrate. In a preferred embodiment, cement is present in an amountgreater than about 50% by weight; Class-C fly ash is present in anamount of about 10 percent to about 20 percent by weight; Class-F flyash is present in an amount of about 10 percent to about 20 percent byweight; and the sodium thiocyanate and/or calcium nitrate is present inan amount of less than about 5 percent by weight.

A further objective of the present invention is to provide a pre-blendcement composition for improved early strength comprising cement, slag,and sodium thiocyanate and/or calcium nitrate. In a preferredembodiment, cement is present in an amount greater than about 50% byweight; slag is present in an amount of about 20 percent to about 30percent by weight; and the sodium thiocyanate and/or calcium nitrate ispresent in an amount of less than about 5 percent by weight.

A further objective of the present invention is to provide a pre-blendcement composition for improved early strength comprising cement,Class-C fly ash, slag, and sodium thiocyanate and/or calcium nitrate. Ina preferred embodiment, cement is present in an amount greater thanabout 50% by weight; Class-C fly ash is present in an amount of about 10percent to about 30 percent by weight; slag is present in an amount ofabout 10 percent to about 20 percent by weight; and sodium thiocyanateand/or calcium nitrate is present in an amount of less than about 5percent by weight.

A further objective of the present invention is to provide a pre-blendcement composition for improved early strength comprising cement,Class-F fly ash, slag, and sodium thiocyanate and/or calcium nitrate. Ina preferred embodiment, cement is present in an amount greater thanabout 50% by weight; Class-F fly ash is present in an amount of about 10percent to about 30 percent by weight; slag is present in an amount ofabout 10 percent to about 20 percent by weight; and sodium thiocyanateand/or calcium nitrate is present in an amount of less than about 5percent by weight.

A further objective of the present invention is to provide a pre-blendcement composition for improved early strength comprising cement,Class-C fly ash, Class-F fly ash, slag, and sodium thiocyanate and/orcalcium nitrate. In a preferred embodiment, cement is present in anamount greater than about 50% by weight; Class-C fly ash is present inan amount of about 10 percent to about 20 percent by weight; Class-F flyash is present in an amount of about 10 percent to about 20 percent byweight; slag is present in an amount of about 10 percent to about 20percent by weight; and sodium thiocyanate and/or calcium nitrate ispresent in an amount of less than about 5 percent by weight.

Silica fume can also be included in any of the pre-blend cements of thepresent invention.

Methods of making concrete from the above compositions are alsodisclosed.

Pre-blend as used herein refers to settable compositions mixed prior tothe addition of water and/or aggregated materials, i.e., a dry mix.Pre-blend cements (also referred to as blended cements) are mixedwithout the addition of water, sand, and/or gravel, and are sold, inbags and/or in tanker loads, for concrete making. The standard forpre-blend cement is specified in ASTM Designation C 595. A majoradvantage of pre-blend include the ability for concrete producer tocustom blend a cement for his own application, e.g., higher strength formultistory building; higher durability for bridges, highways, andparking structures; lower pozzolan content for economic effect, such asmaximum pozzolan content for plants with single silos. The pre-blendcement of the present invention is particularly for making pre-blendcement and should not be confused with ready-mix processes for makingconcrete. The ready-mix processes involve adding water, sand, stone,admixtures, etc. to cement to form concrete, while the pre-blend cementis a dry powder.

DETAILED DESCRIPTION OF THE INVENTION

Several different types of Portland cement are available and all areuseful with the present invention. Type I is the general-purpose varietyand is most commonly employed; Type II Portland cement is used whereprecaution against moderate sulfate attack is important; Type III is ahigh-early strength Portland cement; Type IV is a low heat of hydrationcement for use where the rate and amount of heat generated must beminimized; Type V is a sulfate-resisting cement used only in concreteexposed to severe sulfate action. Although most types of cement areuseful with the present invention, Type III is preferable for the earlystrength application. Commercial blended cements, such as Type I-P,wherein 20% Class-F fly ash is blended with 80% by weight Portlandcement clinker during pulverization should be avoided, because Type I-Pcements do not meet ASTM C595 specification.

Any standard or common Class-F fly ash obtained from boilers and likefurnaces used for the combustion of pulverized coal, particularly of abituminous or anthracite type, and especially from coal-fired,steam-generating plants of electrical utilities, is suitable for use asthe Class-F fly ash component of this invention. Such fly ash shouldhave a combined silica, alumina and ferric oxide content of at leastabout 70% and preferably 80% or higher by weight and a lime (CaO)content below about 10%, usually about 6% by weight or less.

Any standard or common Class-C fly ash obtained from the burning oflignite or subbituminous coal is suitable for use as the Class-C fly ashcomponent of this invention. Such Class-C fly ash generally containsmore calcium and less iron than Class-F fly ash and has a lime contentin the range of 15% to 30%.

In certain embodiments, CF fly ash is used. This is a mixture of Class-Cand Class-F fly ashes, which can be manufactured by adding Class-C flyash and Class-F fly ash together or by the combustion of a mixture ofwestern and eastern coal. An all-western coal produces Class-C fly ash;and an all-eastern coal produces Class-F fly ash. Because of emissionsand environmental concerns, some power plants may burn a mixture ofeastern and western coals. The percentages of eastern and western coalsmay vary according to the needs of the individual power plant, thus,resulting in different ratios of Class-C fly ash to Class-F fly ash.

Likewise, any blast furnace slag is appropriate for the presentinvention. Slag is a non-metallic co-product produced in the productionof iron in a blast furnace. It consists primarily of silicates,aluminosilicates and calcium-alumina-silicates. The molten slag usuallycomprises about twenty percent by mass of iron production. Differentforms of slag products are produced depending on the method used to coolthe molten slag. These products include air-cooled blast furnace slag,expanded or foamed slag, pelletized slag, and granulated blast furnaceslag. Granulated blast furnace slag satisfying ASTM 989 specification ispreferred.

Any sodium thiocyanate is appropriate for the present invention. Sodiumthiocyanate is a salt generally available as colorless or whitecrystals. Sodium thiocyanate is sold in several different grades andforms, depending on the intended end use. Main uses for sodiumthiocyanate are in sectors of industrial chemicals, pharmaceuticals,pesticides, photography, etc. Although any sodium thiocyanate isappropriate for the present invention, cost is a major considerationbecause sodium thiocyanate is available in many grades. Therefore, theleast expensive form of sodium thiocyanate that is effective for thepresent invention is most preferred.

Any calcium nitrate is appropriate for the present invention. Calciumnitrate is a salt generally available as colorless to white, usuallyhydrated, granules, crystals, or powder. Calcium nitrate is sold inseveral different grades and forms, depending on the intended end use.Main uses for calcium nitrate are in sectors of explosive, pesticides,industrial chemicals, etc. Although any calcium nitrate is appropriatefor the present invention, cost is a major consideration because calciumnitrate is available in many grades. Therefore, the least expensive formof calcium nitrate that is effective for the present invention is mostpreferred.

As will be established hereinafter, within the above limits for thecompositions of the invention, the concretes produced therefrom exhibitsubstantially comparable or superior properties for use in generalpurpose cement construction, especially early setting time.

Final concrete mixes using the pre-blend cement of the present inventionmay further contain aggregate materials. The choice of aggregatematerial for concrete mixes using the present blends will pose noproblem to the person skilled in the design of such mixes. The coarseaggregate should have a minimum size of about ⅜ inch and can vary insize from that minimum up to one inch or larger, preferably ingradations between these limits. Crushed limestone, gravel and the likeare desirable coarse aggregates, and the material selected in any caseshould exhibit a considerable hardness and durability inasmuch ascrumbly, friable aggregates tend to significantly reduce the strength ofthe ultimate concrete. The finely divided aggregate is smaller than ⅜inch in size and again is preferably graduated in much finer sizes downto 200-sieve size or so. Ground limestone, sand and the like are commonuseful fine aggregates.

In accordance with the present invention, silica fume can also be addedto the cement mixture to achieve high strength and chloride protectionfor the concrete. Silica fume is preferably used from 5-15 percent byweight.

Other additives can also be used in making concrete using the pre-blendcement of the present invention, including, but is not limited to, waterreducers, accelerators, air entrainment agents, as well as otheradditives that are commonly used in the concrete industry.

The pre-blend mixes of the invention are prepared by homogeneously anduniformly mixing all of the mix ingredients including cement, Class-Ffly ash, Class-C fly ash, slag, and sodium thiocyanate and/or calciumnitrate prior to addition of water and/or aggregate material, such assand and/or gravel. Mixing can be accomplished with mixing techniquescommonly employed in the concrete mix industry. The ultimatecompositions are no more susceptible to undergoing separation duringhandling and storage than are ordinary concrete mixes. They can betransported and stored in the same manner as the ordinary mixes, as canthe individual ingredients. The storage containers should, of course, beclosed to protect the contents thereof from weather.

The following examples are given to illustrate the present invention. Itshould be understood that the invention is not limited to the specificconditions or details described in these examples.

The results in the following examples were actually obtained bypre-blending, in each case, Class-F fly ash, Class-C fly ash, slag,and/or silica fume with sodium thiocyanate and/or calcium nitratetogether to form a pre-blend composition and then combining the blendwith the other mix ingredients. The pre-blend components are added priorto the addition of water. However, the results would be expected to beidentical if the same proportionate amount for each of the component wasadded separately to the remaining dry mix ingredients. The proportionateamounts of the Class-F fly ash, Class-C fly ash, slag, silica fume,sodium thiocyanate and calcium nitrate have been expressed in each casein terms of their relative weight percentages of the pre-blendcomposition.

EXAMPLE 1

TABLE 1 Composition in weight percent Silica Set time Cement Class-FClass-C Slag Fume M* NaSCN Ca(NO₃)₂ Initial Final 60 10 10 15 5 0 0 0135 495 60 10 10 15 5 0 0 0.6 145 410 50 10 15 20 0 5 0 0 210 395 50 1015 20 0 5 0 1 120 285 60 10 10 0 0 20 0 0 60 230 60 10 10 0 0 20 0 0.660 200 50 0 30 0 0 20 0 0 35 240 50 0 30 0 0 20 0 1.2 25 220 50 0 0 40 010 0 0 100 280 50 0 0 40 0 10 0 0.2 115 265 90 10 0 0 0 0 0 0.2 210 30569 0 29 0 0 0 0 2 130 200 70 0 0 30 0 0 0 0.2 210 350 40 0 0 60 0 0 00.2 190 355 65 0 0 30 5 0 0 0.2 175 255 60 10 0 30 0 0 0 0.2 205 300 500 20 30 0 0 0 0.4 210 375 90 0 0 0 0 10 0 0.2 150 250 60 0 0 30 0 10 00.2 140 265 ASTM 595 Specification 45 min. 420 max. *Calcined Metakaolin

Compositions from Table 1 shows that calcium nitrate, in amounts up to1.2 percent (w/w) reduces setting times for cement compositions tocomply with ASTM Designation C595. Applicant has also found that theoptimal amounts for calcium nitrate are between about 0.1-5 percent(w/w). Above this amount, the setting times are too fast to meet theASTM specification. It must be noted that, throughout the examples,because the numbers are approximate, the components of some compositionsdo not add up to exactly 100%; however, they are all within the errorrange of 100±1%.

EXAMPLE 2

TABLE 2 Composition in weight percent Silica Set time Cement Class-FClass-C Slag Fume M* NaSCN Ca(NO₃)₂ Initial Final 60 5 5 20 5 5 0 0 140435 60 5 5 20 5 5 0 0.2 420 345 60 5 5 20 5 5 0.2 0 155 340 50 10 15 200 5 0 0 210 395 50 10 15 20 0 5 0 1 120 285 50 10 15 20 0 5 1 0 140 40050 10 15 20 0 5 0.5 0.5 170 395 70 20 0 0 0 10 0 0 120 300 70 20 0 0 010 0 0.2 130 275 70 20 0 0 0 10 0.2 0 95 310 70 20 0 0 0 10 0.1 0.1 120300 50 0 0 40 0 10 0 0 100 280 50 0 0 40 0 10 0 0.2 115 265 50 0 0 40 010 0.2 0 95 270 50 0 0 40 0 10 0.1 0.1 105 250 45 0 0 36 0 9 0 10 3 1045 0 0 36 0 9 5 5 3 80 ASTM C595 Specification 45 min. 420 max.*Calcined Metakaolin

The trend from Table 2 shows that the higher the calcium nitrate and/orsodium thiocyanate the faster the set time. However, up to a maximumamount of calcium nitrate, the mix hardens too quickly to meet ASTM C595 specification. Interpolation of the data shows that the amount ofnon-chloride accelerators (calcium nitrate and sodium thiocyanate) usedshould not exceed about 5 percent.

EXAMPLE 3

TABLE 3 Composition in weight percent Silica Set time Cement Class-FClass-C Slag Fume M* NaSCN Ca(NO₃)₂ Initial Final Control 220 315 63 0 027 0 0 0 10 6 12 63 0 0 27 0 0 5 5 10 45 45 0 0 45 0 0 0 10 7 15 45 0 045 0 0 5 5 11 50 ASTM C595 Specification 45 min. 420 max. *CalcinedMetakaolin

Table 2 shows accelerator concentration (sodium thiocyanate and/orcalcium nitrate) of 10 percent (w/w) allows the mixes to set up too fastand does not meet the ASTM C595 specification.

EXAMPLE 4

TABLE 4 Composition in weight percent Silica Set time Cement Class-FClass-C Slag Fume M* NaSCN Ca(NO₃)₂ Initial Final 57 9 0 29 0 0 5 0310 >420 50 0 20 30 0 0 1 0 160 315 48 0 19 29 0 0 5 0 195 >420 85 15 00 0 0 0.2 0 190 285 81 14 0 0 0 0 5 0 340 >420 69 0 29 0 0 0 2 0 200 40567 0 29 0 0 0 5 0 120 >420 70 15 15 0 0 0 1 0 240 335 67 14 14 0 0 0 5 0400 >420 50 0 0 50 0 0 0.2 0 160 245 48 0 0 48 0 0 5 0 275 >420 60 10 030 0 0 0.2 0 150 250 57 9 0 29 0 0 5 0 310 >420 50 0 20 30 0 0 1 0 160315 48 0 19 29 0 0 5 0 195 >420 ASTM C595 Specification 45 min. 420 max.*Calcined Metakaolin

Table 4 shows that the accelerating effect of sodium thiocyanate onlyoccurs at concentrations less than 5 percent (w/w). At about 5 percent(w/w) sodium thiocyanate actually retards the setting time of the mixes.From Table 4, the retarding effect is sufficient to produce a mix thatdoes not comply with ASTM Designation C595. This discovery is unexpectedand not previously known in the art.

The above examples clearly show faster setting times of cement mixes bythe addition of less than about 5 percent sodium thiocyanate and/orcalcium nitrate. Importantly, the setting times also meets ASTMspecifications. The improvement is effective not only for cement, butalso for mixes comprising industrial by-products such as Class-F flyash, Class-C fly ash, blast furnace slag, silica fume and combinationsthereof. The invention, however, is not limited to the conditionsillustrated in the examples.

Although certain presently preferred embodiments of the invention havebeen specifically described herein, it will be apparent to those skilledin the art to which the invention pertains that variations andmodifications of the various embodiments shown and described herein maybe made without departing from the spirit and scope of the invention.Accordingly, it is intended that the invention be limited only to theextent required by the appended claims and the applicable rules of law.

1. A pre-blend composition comprising cement and less than about 5percent by weight based on the total composition of sodium thiocyanate,wherein the composition is substantially free of water, and has aninitial setting time of greater than or equal to 45 minutes and a finalsetting time of less than or equal to 420 minutes when the compositionis mixed with water.
 2. The composition of claim 1, wherein the cementis Portland cement.
 3. The composition of claim 1, wherein the cement ispresent in an amount of at least about 50 percent by weight based on thetotal composition.
 4. The composition of claim 1, further comprisingsilica fume.
 5. The composition of claim 4, wherein the silica fume ispresent in an amount of about 5-15 percent by weight based on the totalcomposition.
 6. The composition of claim 4, wherein the silica fume ispresent in an amount of about 10 percent by weight based on the totalcomposition.
 7. The composition of claim 1, further comprising calciumnitrate.
 8. The composition of claim 7, wherein the calcium nitrate ispresent in an amount less than about 5 percent by weight based on thetotal composition.
 9. The composition of claim 1, wherein thecomposition is a dry blend.
 10. A pre-blend composition comprisingcement, slag, and less than about 5 percent by weight based on the totalcomposition of sodium thiocyanate, wherein the composition issubstantially free of water, and has an initial setting time of greaterthan or equal to 45 minutes and a final setting time of less than orequal to 420 minutes when the composition is mixed with water.
 11. Thecomposition of claim 10, wherein the cement is Portland cement.
 12. Thecomposition of claim 10, wherein the cement is present in an amount ofat least about 50 percent by weight based on the total composition. 13.The composition of claim 10, further comprising silica fume.
 14. Thecomposition of claim 13, wherein the silica fume is present in an amountof about 5-15 percent by weight based on the total composition.
 15. Thecomposition of claim 10, further comprising calcium nitrate.
 16. Thecomposition of claim 15, wherein the calcium nitrate is present in anamount of less than about 5 percent by weight based on the totalcomposition.
 17. The composition of claim 10, wherein the slag ispresent in an amount of about 10-20 percent by weight based on the totalcomposition.
 18. The composition of claim 10, wherein the slag ispresent in an amount of about 10-20 percent by weight based on the totalcomposition, and the cement is present in an amount of at least about 50percent by weight based on the total composition.
 19. The composition ofclaim 10, wherein the composition is a dry blend.
 20. A pre-blendcomposition comprising cement, Class-F fly ash, and less than about 5percent by weight based on the total composition of sodium thiocyanate,wherein the composition is substantially free of water, and has aninitial setting time of greater than or equal to 45 minutes and a finalsetting time of less than or equal to 420 minutes when the compositionis mixed with water.
 21. The composition of claim 20, wherein the cementis Portland cement.
 22. The composition of claim 20, wherein the cementis present in an amount of at least about 50 percent by weight based onthe total composition.
 23. The composition of claim 20, furthercomprising silica fume.
 24. The composition of claim 23, wherein thesilica fume is present in an amount of about 5-15 percent by weightbased on the total composition.
 25. The composition of claim 20, furthercomprising calcium nitrate.
 26. The composition of claim 25, wherein thecalcium nitrate is present in an amount of less than about 5 percent byweight based on the total composition.
 27. The composition of claim 20,wherein the Class-F fly ash is present in an amount of about 20-30percent by weight based on the total composition.
 28. The composition ofclaim 20, wherein the Class-F fly ash is present in an amount of about20-30 percent by weight based on the total composition, and the cementis present in an amount of at least about 50 percent by weight based onthe total composition.
 29. The composition of claim 20, furthercomprising slag.
 30. The composition of claim 29, wherein the slag ispresent in an amount of about 10-20 by weight based on the totalcomposition.
 31. A pre-blend composition comprising cement, Class-C flyash, and less than about 5 percent by weight based on the totalcomposition of sodium thiocyanate, wherein the composition issubstantially free of water, and has an initial setting time of greaterthan or equal to 45 minutes and a final setting time of less than orequal to 420 minutes when the composition is mixed with water.
 32. Thecomposition of claim 31, wherein the cement is Portland cement.
 33. Thecomposition of claim 31, wherein the cement is present in an amount ofat least about 50 percent by weight based on the total composition. 34.The composition of claim 31, further comprising silica fume.
 35. Thecomposition of claim 34, wherein the silica fume is present in an amountof about 5-15 percent by weight based on the total composition.
 36. Thecomposition of claim 31, further comprising calcium nitrate.
 37. Thecomposition of claim 36, wherein the calcium nitrate is present in anamount of less than about 5 percent by weight based on the totalcomposition.
 38. The composition of claim 31, wherein the Class-F flyash is present in an amount of about 20-30 percent by weight based onthe total composition.
 39. The composition of claim 31, wherein theClass-F fly ash is present in an amount of about 20-30 percent by weightbased on the total composition, and the cement is present in an amountof at least about 50 percent by weight based on the total composition.40. The composition of claim 31, further comprising slag.
 41. Thecomposition of claim 40, wherein the slag is present in an amount ofabout 10-20 by weight based on the total composition.
 42. Thecomposition of claim 31, wherein the composition is a dry blend.
 43. Apre-blend composition comprising cement, Class-C fly ash, Class-F flyash, and less than about 5 percent by weight based on the totalcomposition of sodium thiocyanate, wherein the composition issubstantially free of water, and has an initial setting time of greaterthan or equal to 45 minutes and a final setting time of less than orequal to 420 minutes when the composition is mixed with water.
 44. Thecomposition of claim 43, wherein the cement is Portland cement.
 45. Thecomposition of claim 43, wherein the cement is present in an amount ofat least about 50 percent by weight based on the total composition. 46.The composition of claim 43, further comprising silica fume.
 47. Thecomposition of claim 46, wherein the silica fume is present in an amountof about 5-15 percent by weight based on the total composition.
 48. Thecomposition of claim 43, further comprising calcium nitrate.
 49. Thecomposition of claim 48, wherein the calcium nitrate is present in anamount of less than about 5 percent by weight based on the totalcomposition.
 50. The composition of claim 43, wherein the Class-F flyash is present in an amount of about 10-20 by weight based on the totalcomposition.
 51. The composition of claim 43, wherein the Class-C flyash is present in an amount of about 10-20 by weight based on the totalcomposition.
 52. The composition of claim 43, wherein the Class-F flyash is present in an amount of about 10-20 by weight based on the totalcomposition, the Class-C fly ash is present in an amount of about 10-20by weight based on the total composition, and the cement is present inan amount of at least about 50 percent by weight based on the totalcomposition.
 53. The composition of claim 43, further comprising slag.54. The composition of claim 53, wherein the slag is present in anamount of about 10-20 by weight based on the total composition.
 55. Apre-blend composition comprising cement and less than about 5 percent byweight based on the total composition of calcium nitrate, wherein thecomposition is substantially free of water, and has an initial settingtime of greater than or equal to 45 minutes and a final setting time ofless than or equal to 420 minutes when the composition is mixed withwater.
 56. The composition of claim 55, wherein the cement is Portlandcement.
 57. The composition of claim 55, wherein the cement is presentin an amount of at least about 50 percent by weight based on the totalcomposition.
 58. The composition of claim 55, further comprising silicafume.
 59. The composition of claim 58, wherein the silica fume ispresent in an amount of about 5-15 percent by weight based on the totalcomposition.
 60. A pre-blend composition comprising cement, slag, andless than about 5 percent by weight based on the total composition ofcalcium nitrate, wherein the composition is substantially free of water,and has an initial setting time of greater than or equal to 45 minutesand a final setting time of less than or equal to 420 minutes when thecomposition is mixed with water.
 61. The composition of claim 60,wherein the cement is Portland cement.
 62. The composition of claim 60,wherein the cement is present in an amount of at least about 50 percentby weight based on the total composition.
 63. The composition of claim60, further comprising silica fume.
 64. The composition of claim 63,wherein the silica fume is present in an amount of about 5-15 percent byweight based on the total composition.
 65. The composition of claim 60,wherein the slag is present in an amount of about 10-20 by weight basedon the total composition.
 66. The composition of claim 60, wherein theslag is present in an amount of about 10-20 by weight based on the totalcomposition, and the cement is present in an amount of at least about 50percent by weight based on the total composition.
 67. A pre-blendcomposition comprising cement, Class-F fly ash, and less than about 5percent by weight based on the total composition of calcium nitrate,wherein the composition is substantially free of water, and has aninitial setting time of greater than or equal to 45 minutes and a finalsetting time of less than or equal to 420 minutes when the compositionis mixed with water.
 68. The composition of claim 67, wherein the cementis Portland cement.
 69. The composition of claim 67, wherein the cementis present in an amount of at least about 50 percent by weight based onthe total composition.
 70. The composition of claim 67, furthercomprising silica fume.
 71. The composition of claim 70, wherein thesilica fume is present in an amount of about 5-15 percent by weightbased on the total composition.
 72. The composition of claim 67, whereinthe Class-F fly ash is present in an amount of about 20-30 percent byweight based on the total composition.
 73. The composition of claim 67,wherein the Class-F fly ash is present in an amount of about 20-30percent by weight based on the total composition, and the cement ispresent in an amount of at least about 50 percent by weight based on thetotal composition.
 74. The composition of claim 67, further comprisingslag.
 75. The composition of claim 74, wherein the slag is present in anamount of about 10-20 by weight based on the total composition.
 76. Apre-blend composition comprising cement, Class-C fly ash, and less thanabout 5 percent by weight based on the total composition of calciumnitrate, wherein the composition is substantially free of water, and hasan initial setting time of greater than or equal to 45 minutes and afinal setting time of less than or equal to 420 minutes when thecomposition is mixed with water.
 77. The composition of claim 76,wherein the cement is Portland cement.
 78. The composition of claim 76,wherein the cement is present in an amount of at least about 50 percentby weight based on the total composition.
 79. The composition of claim76, further comprising silica fume.
 80. The composition of claim 79,wherein the silica fume is present in an amount of about 5-15 percent byweight based on the total composition.
 81. The composition of claim 76,wherein the Class-F fly ash is present in an amount of about 20-30percent by weight based on the total composition.
 82. The composition ofclaim 76, wherein the Class-F fly ash is present in an amount of about20-30 percent by weight based on the total composition, and the cementis present in an amount of at least about 50 percent by weight based onthe total composition.
 83. The composition of claim 76, furthercomprising slag.
 84. The composition of claim 83, wherein the slag ispresent in an amount of about 10-20 by weight based on the totalcomposition.
 85. The composition of claim 76, wherein the composition isa dry blend.
 86. A pre-blend composition comprising cement, Class-C flyash, Class-F fly ash, and less than about 5 percent by weight based onthe total composition of calcium nitrate, wherein the composition issubstantially free of water, and has an initial setting time of greaterthan or equal to 45 minutes and a final setting time of less than orequal to 420 minutes when the composition is mixed with water.
 87. Thecomposition of claim 86, wherein the cement is Portland cement.
 88. Thecomposition of claim 86, wherein the cement is present in an amount ofat least about 50 percent by weight based on the total composition. 89.The composition of claim 86, further comprising silica fume.
 90. Thecomposition of claim 89, wherein the silica fume is present in an amountof about 5-15 percent by weight based on the total composition.
 91. Thecomposition of claim 86, wherein the Class-F fly ash is present in anamount of about 10-20 by weight based on the total composition.
 92. Thecomposition of claim 86, wherein the Class-C fly ash is present in anamount of about 10-20 by weight based on the total composition.
 93. Thecomposition of claim 86, wherein the Class-F fly ash is present in anamount of about 10-20 by weight based on the total composition, theClass-C fly ash is present in an amount of about 10-20 by weight basedon the total composition, and the cement is present in an amount of atleast about 50 percent by weight based on the total composition.
 94. Thecomposition of claim 86, further comprising slag.
 95. The composition ofclaim 94, wherein the slag is present in an amount of about 10-20 byweight based on the total composition.